Desublimer for the recovery of sublimed products, particularly phtalic anhydride, from reaction gases

ABSTRACT

Desublimer for the recovery of sublimed products from reaction gases, consisting of a closed housing for the passage of the reaction gas and a plurality of horizontally mounted rows of finned tubes for the passage of the heating or cooling medium, in which a perforated slider is mounted on each finned tube to allow adjacent finned tubes to bear loosely against each other, the stack of superposed sliders associated with each finned tube being loosely supported on a girder securely attached to the housing.

United States Patent Wirth et al.

[451 Sept. 16, 1975 1 1 DESUBLIMER FOR THE RECOVERY OF SUBLIMED PRODUCTS, PARTICULARLY PHTALIC ANHYDRIDE, FROM REACTION GASES [75] Inventors: Friedrich Wirth, Ludwigshafen;

Gert Buerger, Mannheim; Joachim Wagner, Ludwigshafen; Eberhard Schoenberger, Frankenthal; Harry Kassat, Bochum; Herbert Kolenda, Herbede, all of Germany [73] Assignee: BASF Aktiengesellschaft,

Ludwigshafen (Rhine), Germany [22] Filed: Mar. 7, 1974 [21] Appl. No.: 449,029

[30] Foreign Application Priority Data Mar. 10,1973 Germany 2312088 [52] US. Cl 165/82; 165/162 [51] Int. Cl. F28g 9/00 [58] Field of Search 165/67, 68, 69, 149, 162,

[56] References Cited UNITED STATES PATENTS 1,500,895 7/1924 Rover 165/162 X 1,949,126 2/1934 Light 165/68 X 2,608,388 8/1952 Miller 165/175 X 3,012,761 12/1961 Gardner et a1 165/162 X Primary Examiner-Charles J. Myhre Assistant ExaminerTheophil W. Streule, Jr. Attorney, Agent, or FirmJohnston, Keil, Thompson & Shurtleff [57] ABSTRACT Desublimer for the recovery of sublimed products from reaction gases, consisting of a closed housing for the passage of the reaction gas and a plurality of horizontally mounted rows of finned tubes for the passage of the heating or cooling medium, in which a perforated slider is mounted on each finned tube to allow adjacent finned tubes to bear loosely against each other, the stack of superposed sliders associated with each finned tube being loosely supported on a girder securely attached to the housing.

10 Claims, 9 Drawing Figures SHEET u 0F 1 QOOC DESUBLIMER FOR THE RECOVERY OF SUBLIMED PRODUCTS, PARTICULARLY PHTALIC ANHYDRIDE, FROM REACTION GASES This invention relates to a desublimer for the recovery of sublimed products, particularly phthalic anhydride, from reaction gases, consisting of a closed housing for the accommodation or passage of the reaction gas and a plurality of substantially horizontally mounted rows of finned tubes adapted for the passage therethrough of heating and cooling media alternately, the reaction gas being caused to flow through the housing transversely to the flow of heating or cooling medium in the tubes, the superposed finned tubes being paired off by means of 180 bends interconnecting two superposed pipes at one end thereof, the other ends being provided with connections for the inlet and outlet of the heating or cooling medium giving an alternate arrangement of said connections and 180 bends in the vertical direction, and in which the superposed tubes or rows of tubes are mounted at a distance from each other with a restricted freedom of movement to allow for differences in thermal expansion or contraction.

In prior art desublimers of this kind (German Published Application No. 1,072,965), each row of superposed finned tubes is supported by common hollow bars, each row of tubes being associated with a separate hollow bar. The cross'section of these bars and their distance from each other depend to a large extent on the size of the desublimer, namely on the length over which they are required to support the finished tubes, and on the weight of the said tubes.

In large desublimers, the hollow supporting bars may have outer diameters of up to 120 mm and their distance from each other can be about 1,500 mm. The di ameter of the said bars also determines the minimum distance between any two adjacent superposed rows of pipes so that, for a given capacity of the desublimer, they are an important determining factor for the dimensions and overall volume of said desublimer.

Due to the fact that the fins on the finned tubes are very thin, the supporting bars can support said finned tubes only at their core, which means that appropriate sections of the said tubes must be left unfinned. Since the length of such unfinned sections of the tubes is not only dependent on the outer diameter of the supporting bars and the appropriate tolerances but is also governed by the fact that the individual finned tubes are subjected to considerable thermal expansion or contraction due to the alternating use of heating and cooling agents, which expansion or contraction may vary considerably due to the cross-flow of the gases and said cooling and heating agents, the sections of unfinned tube at each supporting bar possibly being greater in length than the outer diameter of the said supporting bars.

Thus, a considerable portion of effective heat exchanging surface must be omitted in the region of the points of support of the finned tubes by the hollow bars. To compensate for this drawback, it is necessary to increase the size of the finned tubes, which in turn leads to an increase in size of the entire desublimer. Apart from this disadvantage, there is partial impairment of the cooling action in the desublimer, since parts of the gas stream preferentially flow through the unfinned tube sections due to the low resistance to flow at these points, and these portions of the gas stream are thus not cooled to the same extent as those portions which flow past the surfaces of the fins. Since local reductions in the cooling action are attended by a similar reduction in the deposition of product, the finless paths between the tubes are the cause of inadequate efficiency of the entire desublimer in relation to the theoretically depositable amount of product.

The disadvantages of the prior art method of supporting the finned tubes in the known desublimer may be summarized as follows:

1. Overlarge distances between the individual superposed rows of finned tubes on account of the goodsized supporting bars bearing each row of finned tubes separately resulting in a corresponding increase in the total volume and thus in the cost of construction.

2. Necessity to omit a substantial portion of the theoretically available effective heat exchanging surface due to the fact that unfinned tube sections of adequate length must be provided in the region of the supporting bars, resulting in a corresponding decrease in the heat exchange efiiciency in relation to the total volume of the finnes tubes used.

3. Reduced cooling due to the lanes produced by the supporting bars at the points where they support the finned tubes, resulting in reduced efficiency of the desublimer.

It is an object of the present invention to improve the method of supporting the finned tubes whilst obviating the above drawbacks by arranging for the volume of finned tubes used to be utilized to an optimum extent for heat exchange and thus for the deposition of product and by making it possible for the individual finned tubes to expand or contract to various degrees independently of each other without giving rise to uncontrollable thermal stresses.

This object is achieved by the present invention, which is characterized in that sliders with cagetype perforations are mounted on the finned tubes to form box-like elements thereabout, disposed in the same positions on each finned tube and at least in the end regions of said tubes, by means of which sliders each finned tube is loosely supported by at least the vertically adjacent slider beneath it, the stacks of directly superposed sliders associated with all rows of tubes or all rows of tubes within each group being loosely supported by common girders securely attached to the housing.

In this way the loads of the superposed finned tubes are borne by the sliders, which directly transfer the total load to the girders. Since the sliders rest loosely on each other, it is possible for the tubes to move relatively to each other within the appropriate limits on account of differences in thermal expansion or contraction, the distance between the superposed finned tubes being at a minimum.

Since the stack of superposed sliders is supported only at its lower end by a girder common to the entire row of tubes, this method of support has no detrimental effects on the efficiency of the desublimer. On the other hand, the invention makes economical prefabrication of appropriately formed sets of finned tubes possible and provides a much simpler method of mounting the finned tubes in the housing. Moreover, the replacement of a defective finned tube or set of finned tubes is simpler in a desublimer of the invention,

Preferably, the finned tubes horizontally adjacent each other in each row are loosely supported or guided by the sliders.

In the case of large-capacity desublimers, it is possible within the scope of the invention to arrange the rows of finned tubes in superposed groups and to provide separate girders for each group.

According to the invention, the sliders, which enclose the finned tubes only over a specific length thereof, have a rectangular cross-section of a similar shape and size as the fins and have notch-like recesses in their end walls, which recesses are of a similar shape and size as the cross-section of the core of the finned tubes and by means of which recesses the sliders are directly supported by the said cores in a region between two successive fins. In order to allow the reaction gas to pass substantially unhindered to the heat-exchanging fins enclosed by the sliders and also in order to prevent deposits from clogging up the interior of the sliders during the heating or melting operation, all of the side walls of the sliders which are parallel to the longitudinal axis of the tube are provided with perforations of as large a size as possible. Although it is usually sufficient to provide perforations having a total area equal to 30 percent of the total area of said walls, it is recommended that the number or size of the perforations be increased greatly, this being easier to realize, the thicker the metal plating is of which the sliders are made. At a wall thickness of about 3 mm, the total area of the perforations is preferably 50 percent of the total area of said walls, if not more.

The perforations may be of any desired shape, e.g. they may be in the form of slots or round holes. Prefer ably, however, the perforations are in the form of regular octagons or octagons elongated in one axis. We have found that perforations of this shape effect a good compromise between perforations of maximum size and adequate load-bearing capacity of the sliders.

The sliders securely mounted on the finned tubes in at least the end regions thereof advantageously have a length of at least about 40 mm and not more than about 100 mm and cover from at least three to not more than about fins depending on the spacing of the fins, which may be from 5 to 20 mm.

In order to pack the finned tubes as closely as possible, the side-to-side dimensions of the sliders are such that their vertical side walls bear snugly against the vertical edges of rectangular fins or touch round fins tangentially. The horizontal side walls of the sliders, however, are advantageously in spaced relationship to the horizontal fin edges, the free space being kept as small as possible, preferably from about 5 mm to not more than mm.

The invention is applicable irrespective of the crosssectional shape of the core of the finned tube. However, in principle, tubes having rectangular fins are to be preferred over tubes having round fins.

According to a preferred embodiment, the sliders are composed of two symmetrical, upper and lower halves of U-shaped cross-section and, when they have been placed over the finned tube, are welded along the line of abutment of the edges of the two halves. In this way the finned tubes, together with the sliders irremovably mounted thereon in at least the end regions thereof, form prefabricated units.

The separate halves of the sliders may be simply made by punching perforated blanks from metal sheeting and bending parts thereof at right angles so as to form a box having side walls and end walls, of which the end walls, which are shorter than the side walls and are shaped at the end edges to match the cross-section of the core of the finned tubes, form the distance pieces for the fixed support of the sliders on the finned tubes.

The invention is illustrated with reference to a preferred embodiment shown in the accompanying drawing, in which FIG. 1 is a side elevation of the desublimer with part of the housing cut away;

FIG. 2 is an end view of the desublimer shown in partial cross-section taken on the line II-II in FIG. 1;

FIGS. 3 to 6 are a longitudinal section, an elevation,-

a plan view and a cross-section respectively of the sliders mounted on the finned tubes;

FIG. 7 corresponds to FIG. 6 but shows a different embodiment;

FIG. 8 is a plan view of a punched blank ready for bending into one half of a slider and FIG. 9 is a perspective view of a slider mounted a finned tube.

In FIGS. 1 and 2, the housing of the desublimer, which is substantially in the form of a cube, is designated by the reference numeral 1 and the finned tube system is designated by 2.

The base 3 and cover 4 of the housing are conical. 5 designates the inlet connection for the reaction gas in the base 3 and 6 designates the outlet connection in the cover 4. The product which melts off the finned tubes during the heating or melting phase is withdrawn through the central outlet 7 in the base 3 of the hous- As may be seen from FIGS. 1 and 2, the finned tubes 8 are arranged in superposed paired rows, the superposed finned tubes of each pair being interconnected at one end by a bend 9 so that each pair forms a hairpin-like structure, whilst the other end of each pipe in each pair is provided with connecting means for the inlet and outlet lines carrying the heating or cooling medium. Said connecting means consist of connections 10 for the inlet line and connections 10a for the outlet line and also of distributor or collecting chambers 11 and 11a which interconnect the free ends of each row of tubes.

The heating and cooling media are advantageously oil and water, the average temperature of the cooling medium in the depositing phase being about 50C, whilst the average temperature of the heating medium for melting the product is about 200C.

Finally, it may be seen from FIGS. 1 and 2 that cage like perforated sliders 12 are placed one at each end of each finned tube 8 and also one at a point mid-way along each finned tube, which sliders 12 enclose said portions of the finned tubes to form a box around them. The vertically adjacent finned tubes support each other, loosely, by means of said sliders, lateral guiding or support of each slider being effected by the horizontally adjacent finned tube in each row, as can be seen from FIG. 2. The sliders 12 on each of the finned tubes form columns of sliders stacked directly one upon the other, and these columns, going down through each row of tubes, are supported, loosely, at their bottom end, on common girders 13 consisting of two channels welded together and firmly secured to the wall of the housing in the lower region of the housing.

A modification of the embodiment shown consists in subdividing the rows of finned tubes within the housing to form superposed groups of finned tubes, each group having its own girders.

FIGS. 3 to 9 illustrate the form of the sliders l2 and the method of attaching them to the finned tubes 8.

In FIGS. 3 to 6 the tubes 8 have a substantially rectangular cross-section rounded at the corners and possess rectangular fins 8a. The sliders 12 have a rectangular cross-section of approximately the same size as the fins, the vertical side walls of the sliders being close to the lateral edges of the fins, whilst a space of a few millimeters is left between the horizontal walls of the sliders and the horizontal edges of the fins. FIGS. 4 and 5, in particular, reveal the relatively large perforations in all of the side walls of the box-like slider, which perforations 14 have the form of a regular octagon. The total area of these perforations I4 is equal to about 50 percent of the total area of said slider walls.

The end walls 120 of the box-like sliders are recessed at their lower end to match the cross-section or profile of the tubes 8 at their core, the recesses allowing the sliders to fit over and be supported by said cores. They also serve as distance pieces and props for transferring the load of the entire finned tube system to the bottom girders l3 and are dimensioned accordingly.

The sliders 12 associated with each finned tube support each other via their horizontal side walls 15 which bear flat against each other but allow for relative movement of the sliders. Thus, the tubes or sliders can move relatively to each other in the course of thermal expansion or contraction without any detriment to the support of the finned tubes by the bottom girders.

As is clearly shown in FIG. 9, the sliders 12 consist of two symmetrical upper and lower box-like halves of U-shaped cross-section, which halves, after they have been placed over the finned tube, are welded together along their abutting edges at 16 so as to form a closed unit together with the finned tube 8, 8a.

In this case, the perforations 14 are round as a variation of the embodiment shown in FIGS. 3 to 6.

Manufacture of the two halves of the slider 12 is effected by punching out a blank 17 of approximately 3 mm thick steel plate and shaped approximately as shown diagrammatically in FIG. 8, complete with perforations 14. The blank is then bent at right-angles along the lines designated by 18 so as to give the box shape as illustrated in FIG. 9 with reference to the one half of the slider drawn in unbroken lines and also with reference to the complementary half indicated in dot dash lines. FIG. 9 clearly shows how the end walls 12a bear against the core 8a of the finned tube by means of their recesses. In this position, the edges of the side walls abut each other so that the two halves of the slider may be welded together in a satisfactory manner.

The embodiment illustrated in FIG. 7 differs from that shown in FIGS. 3 to 6 merely in the fact that the tubes have a circular cross-section at their core and also possess round fins, the cross-section of the slider being approximately square in this case.

We claim:

I. A desublimer for the recovery of sublimed products, anhydride, from reaction gases, consisting essentially of a closed housing for the accommodation or passage of the reaction gas and a plurality of substantially horizontally mounted rows of finned tubes adapted for the passage of heating or cooling media therethrough alternately, the reaction gas being caused to flow through the housing transversely to the flow of heating or cooling medium in the tubes, the superposed finned tubes being paired off by means of 180 bends interconnecting two superposed tubes at one end thereof, the other ends being provided with connections for the inlet and outlet of the heating or cooling medium giving an alternate arrangement of said connections and 180 bends in the vertical direction, and in which the superposed tubes or rows of tubes are mounted at a distance from each other with a restricted freedom of movement to allow for differences in thermal expansion or contraction, wherein sliders with cage-type perforations are mounted on the finned tubes to form box-like elements thereabout, disposed in the same positions on each finned tube and at least in the end regions of said tubes, by means of which sliders each finned tube is loosely supported by at least the vertically adjacent slider beneath it, the stacks of directly superposed sliders associated with all rows of tubes or all rows of tubes within each group being loosely supported by common girders securely attached to the housing.

2. A desublimer as set forth in claim 1, wherein the finned tubes laterally adjacent each other within each row of tubes are loosely supported or guided by each other by means of said sliders.

3. A desublimer as set forth in claim 1, wherein the rows of finned tubes disposed within the box-shaped housing are subdivided into vertical groups, each of which has its own supporting girders.

4. A desublimer as set forth in claim 1 wherein the sliders surrounding the finned tubes over a specific length thereof have a rectangular cross-secti0n matching the size and shape of the fins and are supported by the core of the finned tubes between two successive fins by'means of the end walls of the sliders which are provided with recesses matching the cross-section of said core, all of the slider side walls which are parallel to the longitudinal axis of the tubes being provided with perforations having a total area which is at least 30 percent and is preferably about 50 percent of the total area of the said slider walls.

5. A desublimer as set forth in claim 4, wherein the said perforations are in the form of regular octagons or octagons which are elongated in the direction of the longitudinal axis of the slider.

6. A desublimer as set forth in claim 4, wherein the sliders have a length of from about 40 mm to not more than about mm and enclose from at least three to approximately 10 fins depending on the fin spacing.

7. A desublimer as set forth in claim 4, wherein the vertical side walls of the sliders bear snugly against the vertical edges of rectangular fins or touch round fins tangentially.

8. A desublimer as set forth in claim 4, wherein the horizontal side walls of the sliders are spaced from the horizontal edges of the fins by preferably from 5 mm to not more than 15 mm.

9. A desublimer as set forth in claim 1 or any of the following claims, wherein the slider is composed of two symmetrical upper and lower halves of U-shaped crosssection, which halves, after they have been placed over the finned tubes, are welded together along their abutting edges.

10. A desublimer as set forth in claim 9, wherein the halves of the sliders with perforations in their side walls are made by punching out a blank which is then bent at rightangles to form a box having side walls and end walls, which end walls are shorter than the side walls and have edges shaped to match the cross-section of the core of the finned tubes and form distance pieces for fixed support on the finned tubes. 

1. A DESUBLIMER FOR THE RECOVERY OF SUBLIMED PRODUCTS, ANHYDRIDE, FROM REACTION GASES, CONSISTING ESSENTIALLY OF A CLOSED HOUSING FOR THE ACCOMODATION OR PASSAGE OF THE REACTION GAS AND A PLURALITY OF SUBSTANTIALLY HORIZONTALLY MOUNTED ROWS OF FINNED TUBES ADAPTED FOR THE PASSAGE OF HEATING OR COOLING MEDIA THERETHROUGH ALTERNATELY, THE REACTION GAS BEING CAUSED TO FLOW THROUGH THE HOUSING TRANSVERSELY TO THE FLOW OF HEATING OR COOLING MEDIUM IN THE TUBES, THE SUPERPOSED FINNED TUBES BEING PAIRED OFF BY MEANS OF 180* BENDS INTERCONNECTING TWO SUPERPOSED TUBES AT ONE END THEREOF, THE OTHER ENDS BEING PROVIDED WITH CONNECTIONS FOR THE INLET AND OUTLET OF THE HEATING OR COOLING MEDIUM GIVING AN ALTERNATE ARRANGEMENT OF SAID CONNECTION AND 180* BENDS IN THE VERTICAL DIRECTION, AND IN WHICH THE SUPERPOSED TUBES OR ROWS OF TUBES ARE MOUNTED AT A DISTANCE FROM EACH OTHER WITH A RESTRICTED FREEDOM OF MOVEMENT TO ALLOW FOR DIFFERENCES IN THERMAL EXPANSION OR CONTRACTION WHEREIN SLIDES WITH CAGE-TYPE PERFORATIONS ARE MOUNTED ON THE FINNED TUBES TO FORM BOX-LIKE ELEMENTS THEREABOUT, DISPOSED IN THE SAME POSITION ON EACH FINNED TUBE AND AT LEAST IN THE END REGIONS OF SAID TUBES, BY MEANS OF WHICH SLIDERS EACH FINNED TUBE IS LOOSELY SUPPORTED BY AT LEAST THE VERTICALLY ADJACENT SLIDER BENEATH IT, THE STACKS OF DIRECTLY SUPERPOSED SLIDERS ASSOCIATED WITH ALL ROWS OF TUBES OR ALL ROWS OF TUBES WITHIN EACH GROUP BEING LOOSELY SUPPORTED BY COMMON GIRDERS SECURELY ATTACHED TO THE HOUSING.
 2. A desublimer as set forth in claim 1, wherein the finned tubes laterally adjacent each other within each row of tubes are loosely supported or guided by each other by means of said sliders.
 3. A desublimer as set forth in claim 1, wherein the rows of finned tubes disposed within the box-shaped housing are subdivided into vertical groups, each of which has its own supporting girders.
 4. A desublimer as set forth in claim 1 wherein the sliders surrounding the finned tubes over a specific length thereof have a rectangular cross-section matching the size and shape of the fins and are supported by the core of the finned tubes between two successive fins by means of the end walls of the sliders which are provided with recesses matching the cross-section of said core, all of the slider side walls which are parallel to the longitudinal axis of the tubes being provided with perforations having a total area which is at least 30 percent and is preferably about 50 percent of the total area of the said slider walls.
 5. A desublimer as set forth in claim 4, wherein the said perforations are in the form of regular octagons or octagons which are elongated in the direction of the longitudinal axis of the slider.
 6. A desublimer as set forth in claim 4, wherein the sliders have a length of from about 40 mm to not more than about 100 mm and enclose from at least three to approximately 10 fins depending on the fin spacing.
 7. A desublimer as set forth in claim 4, wherein the vertical side walls of the sliders bear snugly against the vertical edges of rectangular fins or touch round fins tangentially.
 8. A desublimer as set forth in claim 4, wherein the horizontal side walls of the sliders are spaced from the horizontal edges of the fins by preferably from 5 mm to not more than 15 mm.
 9. A desublimer as set forth in claim 1 or any of the following claims, wherein the slider is composed of two symmetrical upper and lower halves of U-shaped cross-section, which halves, after they have been placed over the finned tubes, are welded together along their abutting edges.
 10. A desublimer as set forth in claim 9, wherein the halves of the sliders with perforations in their side walls are made by punching out a blank which is then bent at right-angles to form a box having side walls and end walls, which end walls are shorter than the side walls and have edges shaped to match the cross-section of the core of the finned tubes and form distance pieces for fixed support on the finned tubes. 